The present invention relates to a method of forming an interlayered clay catalyst, and more particularly the use of a soluble carbohydrate as a swelling agent in the formation of such a clay catalyst.
The clay minerals, especially natural and synthetic smectites such as bentonite, montmorillonite and hectorite have a layered structure which can be schematically represented as a sandwich comprised of two outerlayers of silicon tetrahedra and an a inner layer of alumina octahedra. These sandwichs or platelets are stacked or layered one upon the other to yield the unit cells of the clay. Generally, the platelets have basal spacings of about 9.6 angstroms. Swelling of these clays is possible because the parallel lamellae in these structures are bonded to each other not covalently but by Van der Waals and electrostatic forces. There has been a considerable amount of work done to increase the basal spacings of the platelets by a fixed, controlled amount up to about 30 or 40 angstroms. Various polar materials such as water, glycols and amines have been added in an attempt to produce this wider separation. However, such materials tend to be unstable at high temperatures which results in the collapse of the platelets.
More recently, pillars of various metals, generally metal oxide complexes, have been added to the clays to increase the interplatelet distances. These are generally more stable towards heat. In U.S. Pat. No. 4,367,163, pillars of silica have been added to smectites for this purpose, by the use of a solvent to swell the clay, and ionic silicon complex impregnates to form the pillars. In U.S. Pat. No. 4,176,090, pillars of stable inorganic polymers of oxides of metals such as aluminum, zirconium or titanium were added. Other methods of forming pillared catalyst are set forth in U.S. Pat. Nos. 4,248,739 and 4,238,364.
However, the prior art methods of forming the clay having the desired distances between platelets have involved many steps. Multistep processes are not suitable for the production of large quantities of the desired pillared clays, since such processes require the expenditure of large quantities of energy. Further, many prior art processes use expensive and difficult to manufacture reactants, increasing the difficulty of formulating a useful commercial process.